The color of human hair is due to the presence within its structure of discrete natural pigment particles--the melanins. The study of melanins and melanogenesis has intensified in the last 40 years, accompanied by some interest in the dyeing of hair with such materials that most closely resemble the natural materials which contribute the color to hair. The biosynthesis of melanin involves conversion of tyrosine via dihydroxyphenylalanine (dopa) to melanin through a number of intermediate steps, including 5,6-dihydroxyindole, to melanin.
In addition to the general desirability of dyeing hair in a simple fashion and with a dye which is the closest to the material that contributes the natural coloration of hair, a requirement also exists for a hair colorant which can also serve, if desired, as a temporary hair color which can be applied and removed at will and which can be applied in a reliable and fast manner.